In the case of radio systems, in particular wire-free communication systems, which allow frequency spreading by transmission of data on different frequency channels, for example frequency hopping in the case of Bluetooth, it is possible to mask out specific frequency channels in order in this way to avoid interference influences during the transmission process. In the case of so-called adaptive frequency hopping methods (AFH), the masking out of the frequency channels is automated, and is matched to the frequency channel. A distinction is generally drawn between two approaches for such classification and qualification of a frequency channel, and one of these two approaches is selected for masking out a frequency channel.
In a first approach the connection to be adapted (for example Bluetooth) is changed so as not to interfere with a further connection (for example WLAN=Wireless Local Area Network). In the second approach, the procedure is for the connection to be adapted (for example Bluetooth) to be changed such that any possible interference from another connection has as little interference influence as possible. In this second approach, an assessment of the bit error rate or data packet error rate on the channels, for example, may be used for this purpose. In the first approach mentioned above, the field strength can be determined at times at which the connection to be adapted is not active, in order in this way to obtain information about the activity and the use of the frequency channels by another radio system.
In the case of the second approach mentioned above, it is possible, for example, to provide for a bit error rate measurement or a data packet error rate measurement always to be carried out during the reception of data or data packets, respectively, for qualification of a frequency channel. If the bit error rate measurement or data packet error rate measurement results in a high value relative to a comparison value, this frequency channel is subsequently inhibited, or is masked out for data transmission on this frequency channel, so that no more communication takes place on this frequency channel, since an interference source can be assumed, or the proportion of interference on this frequency channel is too high.
One major disadvantage of this procedure is that it is impossible to decide with adequate confidence the extent to which an interference source or an excessively high proportion of noise is actually present on the frequency channel. This is because it is also possible to measure a high bit error rate or data packet error rate because the two units in the radio system which are communicating with one another (for example, two Bluetooth appliances) are relatively far away from one another so that, as a result of this fact, the received signal or data signal can no longer be sampled without errors. An excessively high proportion of interference on the frequency channel will thus be determined incorrectly in this case, with a frequency channel in consequence possibly being inhibited even though no interference source or excessively high proportion of interference is actually present. Since, in particular, this cause of an increased bit error rate or data packet error rate does not have a frequency-selective effect, this would result in this case in an accumulation of incorrect decisions relating to the masking out of frequency channels, and would thus lead to a considerably greater number of frequencies and frequency channels which would no longer be used.
A further major disadvantage is that a single field strength determination, as is possible in the first approach mentioned above, is feasible only at times at which the measuring unit is authorized to transmit data. Furthermore, this is also possible only to a very restricted extent with respect to the number of channels, and is generally possible only for one channel in the vicinity of the transmission channel, or even only for the actual transmission channel itself. Thus, on the one hand, the measurement process can be carried out only at those times at which the measuring unit is authorized to transmit. On the other hand, the information about the overall frequency band that is available through the channels also depends quite significantly on the transmission data throughput rate.
German-Laid Open Specification DE 101 23 639 A1 discloses a method for channel selection and for digital data transmission via a wire-free communication connection. In this case, two or more channels are provided for data transmission, via which a first and a second transmitting/receiver unit communicate without the use of wires. The digital data communication via a wire-free communication connection is provided by means of data packets that are transmitted sequentially on a number of frequency channels. The communication quality of each frequency channel is recorded, and is compared with a quality criterion that can be predetermined. Channels with an inadequate communication quality are replaced by previously unused channels, and/or the amount of control data contained in each data packet is selected as a function of the recorded overall quality of the communication connection. In the case of the methods that are used in a cordless telephone system, only a general quality figure of merit is determined for a frequency channel, and is compared with a quality criterion. The decision as to whether a frequency channel is thus used or is masked out for data transmission can thus be made only on a very inadequate and uncertain basis. The determination of the proportion of interference on a frequency channel and whether the frequency channel is identified and classified as an interference source can thus be made only in a very inadequate manner by using these known methods. Furthermore, no field strength measurement is carried out as information for a selection decision in this method.